An enhanced beamsteering algorithm based on MVDR for a multi-channel parametric array loudspeaker array

A multi-channel parametric array loudspeaker (PAL) array can steer an audio beam using a digital signal processing technique. However, it faces the challenge posed by grating lobes in the ultrasonic radiation pattern, which leads to unwanted sidelobes in the steering audio beam when the Nyquist criterion is not satisfied due to short ultrasonic wavelengths. As a result, the audio beam not only fails to steer in the desired direction but also loses its inherent advantage of high directivity when using a beamsteer with a delay-and-sum (DAS) structure. This work proposes an enhanced beamsteering algorithm to suppress the sidelobes by optimizing the channel weight coefficients. The nonlinear optimization problem is transformed into a linear expression, making the minimum-variance-distortionless-response (MVDR) algorithm applicable. Both simulations and experiments validate the effective suppression of sidelobes and the mitigation of sound fuzziness within the range from the sidelobe to the mainlobe. The audio beam successfully steers in the desired direction and maintains a high directivity. However, the performance of the algorithm deteriorates at high audio frequencies due to the inherent physical limitations of wave interference in sound field control strategies.